The present invention relates to a separator for an electrochemical fuel cell and a method for producing the separator. A separator comprising a conductive metal provides a path for a fuel gas or an oxidative gas to an electrode by contacting the electrode, and the separator functions as a wall of a unit cell of the electrochemical fuel cell.
Previously, close-grained carbon graphite having a high conductivity and gas impermeability is, for example, coated on both surfaces of a separator made of a metal in an electrochemical fuel cell, as proposed in Japanese Laid-Open Patent Application No. 8-222237. This separator is produced by the steps as mentioned below. First, closed-grained graphite is coated on both surfaces of a metal plate made of aluminum, stainless steel, or etc. Next, a plurality of projections are shaped on a surface of the coated metal plate by an embossing or dimple-machining.
In the above-mentioned separator, the closed-grained carbon graphite could come off easily from the metal plate, because the contact between the metal plate and the close-grained graphite is not strong. Accordingly, reliability of the separator for rust resistance is low. Furthermore, since it is difficult to coat the closed-grained graphite uniformly on the metal plate, electrical resistance of the separator is high because of the coating, and the performance of the fuel cell deteriorates.
It is thus one object of the present invention to solve the aforementioned problems. Another object of the invention is to provide a separator which has high reliability for rust resistance of a metal plate. Another object of the invention is to provide a separator which restrains electrical resistance of the separator low and to provide an electrochemical fuel cell with a sufficient performance. Other object is to restrain adsorption of a metallic ion melted out from the separator to an electrolyte membrane. Furthermore, other object is to produce the aforementioned separator easily.
According to one aspect of the invention, as the first embodiment of a separator for an electrochemical fuel cell, the separator provides a path for a fuel gas or an oxidative gas to an electrode and functions as a wall of a unit cell, and the separator contacts an electrode. The separator includes a conductive metal plate, a conductive coating membrane which coats the conductive metal plate where the separator contacts the electrode, and a tight coating membrane which coats the conductive metal plate where the conductive coating membrane is not on the conductive metal plate. Incidentally, the fuel gas indicates a gas mainly containing hydrogen, and the oxidative gas indicates a gas mainly containing oxidant.
It is available that a conductivity of the conductive coating membrane is higher than the coating membrane, and the tight coating membrane has a tighter adhesion to the conductive metal plate than the conductive coating membrane.
The conductive coating membrane comprises, for example, carbon, a precious metal, or an alloy of nickel and chromium. The tight coating membrane, for example, comprises a close-grained resin.
In this embodiment, since the tight coating membrane contacts closely to the conductive metal plate with its tighter adhesion, the separator reliably prevents the conductive metal plate from rusting due to coming-off of the coating membrane including the conductive coating membrane and the tight coating membrane. Moreover, since the conductive coating membrane has a high conductivity, the electrical resistance of the separator caused by coating the coating membrane is restrained low. Consequently, the performance of the fuel cell is high.
As a modified embodiment to the first embodiment, the tight coating membrane includes a coating layer which is made of the same material as the conductive coating membrane, and an adhesive layer which bonds the coating layer to the conductive coating metal plate with a tighter adhesion than between the conductive coating membrane and the conductive metal plate. It is available that the coating layer comprises a heat expansional graphite seat or porous resin film permeated by carbon powder. It is also available that the adhesive layer comprises adhesive of epoxy resin or phenol resin.
Since the tight coating membrane includes an adhesive layer and the adhesive layer bonds the coating layer to the conductive metal plate with a tighter adhesion, the rust of the conductive metal plate caused by coming-off of the coating layer can be avoided with high reliability. Since the conductive coating membrane has a high conductivity, the electrical resistance of the separator is restrained low. The performance of the fuel cell with the separator is, then, high.
Next, as a second embodiment, a separator for an electrochemical fuel cell, provides a path for a fuel gas or an oxidative gas to an electrode and functions as a wall of a unit cell. The separator contacts the electrode and the separator include a conductive metal plate, a tight layer which is coated on the conductive metal plate, and a conductive coating membrane which is coated on the tight layer where the separator contacts the electrode. Furthermore, the tight layer bonds the conductive coating membrane to the conductive metal plate, and the tight layer comprises a high conductivity metal and has a heat softened high deformation characteristic.
Since the conductive coating membrane closely contacts the conductive metal plate owing to the heat softened high deformation characteristic of the tight layer, the rust problem caused by coming-off of the conductive coating membrane from the conductive metal plate can be avoided. Furthermore, since the conductive coating membrane closely contacts the conductive metal plate and the tight layer comprises a high conductivity, electrical resistance of the separator can also be restrained low.
Next, as a third embodiment, a separator for an electrochemical fuel cell provides a path for a fuel gas or an oxidative gas to an electrode and functions as a wall of a unit cell. The separator contacts the electrode, and the separator has a tight coating membrane made of a material being able to adsorb a metallic ion melted out from the conductive metal plate. The tight coating membrane coats the place where the separator forms a path for a fuel gas or an oxidative gas. It is available that the tight coating membrane is made of Schiff basic chelate resin and/or oxine chelate resin.
Since the tight coating membrane which forms the path for the fuel gas or the oxidative gas adsorbs a metallic ion, even though the metallic ion is melted out from the separator, an electrolyte membrane does not adsorb the metallic ion. The performance of the fuel cell is then high.
Next, a method for producing the separator of the first embodiment is explained briefly. The method comprises a step of placing a conductive coating membrane on a conductive metal plate where the separator contacts an electrode, a step of placing a tight coating membrane on the conductive metal plate where the conductive coating membrane is not on the conductive metal plate, a step of heating and pressing the conductive coating membrane and the tight coating membrane with the conductive metal plate. As mentioned above, the tight coating membrane has a tighter adhesion to the conductive metal plate than the conductive coating membrane.
By this method, since the conductive coating membrane closely contacts the conductive metal plate by heating and pressing the conductive metal plate, the conductive coating membrane, and the tight coating membrane, the separator which has high anti-rust and low electrical resistance characteristics is produced.